Simply a put, a few lasers shining out onto the horizon, which let off an alarm whenever they hit something. Sort of like the laser alarms in a banks vault. They should not hit anything, as they will be shining well above the water line. This will be located on a tower, with a leveling system to prevent
the ships rocking from forcing the lasers to contact the waterline. The lasers will always be level with the earth.

Possible problem: birds flying in front of the laser.

I just watched a show on the History channel about Rogue waves, and they seem very real considering all the sources and incidents.

They're real enough. The problem you will have is that your system will only detect such waves as they cross the true horizon - depending on how tall your vessel is, that will vary a lot. And then you have to confirm if it's a real alarm, and then maneuver out of the way - no easy task for a big vessel, and if you react to every alert as real you would potentially waste a lot of time and fuel.

These lasers would be mounted on land, not boats. A laser beam
can't set off an alarm unless there's a sensor at the far end. Birds
though could be ignored because interuption would be momentary
vs. Sustained. I bun ya.

I suppose the laser tracker could detect the relative positions of hand, elbow and smile. Trigonometric algorithms compute a score based on velocity and seperation, with HM the Q as a fixed reference. If the score deviates more than a set amount, a klaxon sounds.